Metallic article



Patented May 23, 1939 ITED STATES PATENT JOE-ICE Walter Schubardt,

Mannheim, Germany, as-

signors to I. G. Farbenindustrle Aktiengesellschaft, Frankfort-on-the-Main, Germ No Drawing. Application October 25, 1934, Serial No. 749,922. In Germany March 26, 1928 vzclaims.

The present invention relates to metallic articles, more particularly such as consist of or contain nickel, the said articles being diflerent from, and superior to, any metallic articles of substantially the same composition which have been known prior to the present invention. Throughout this application and the appended claims the term "articles is used in a broad sense including not only worked pieces of nickel or nickel alloys, but also coherent lumps of more or less irregular shape which may serve for making worked pieces therefrom, but is not meant to include nickel or nickel alloys in the form of coarse or fine powder.

More particularly, this invention relates to pure nickel articles as well as to articles consisting of nickel alloys, especially those with iron, chromium, manganese, copper or several of these elements.

In order that our invention and the advantages 2o inherent therewith may be fully understood it may be convenient first to give a brief summary of the prior art and the disadvantages which are experienced in the known processes.

Prior to the present invention, nickel articles have been prepared mainly from the so-called cube-nickel or from the small nickel balls prepared by the Mond process.

Cube-nickel is prepared by intimately mixing nickel oldde and carbon, making the mass into cubes and heating to a reduction temperature. The resulting nickel contains copper and at least ifrom 0.2 to 0.3 per cent of carbon and often further impurities. In order to make nickel articles from this material, it must be subjected to a melting operation and, in order to prevent oxidation, an addition of manganese or magnesium must be made; furthermore certain constituents of the material of the crucible in which the melting operation is carried out, often pass into the molten metal which is, moreover, liable to take up impurities from the heating medium used for melting. Such melting operation therefore leads to more or less substantial contamination of the nickel used as initial material which, moreover, is impure itself.

The small nickel ballsfrom .the Mond process, i. e., a process in which nickel carbonyl is thermally decomposed on small nickel particles kept in continuous movement, also require a melting operation for being worked into nickel articles, in which melting process the same disadvantages are experienced as in the case of cubenickel.

Metallic nickel may also be produced-by elec- 55 trolyzing solutions of nickel salts. The resulting nickel can as a rule be worked into nickel articles only by a melting operation which is attended not only with the disadvantages discussed above, but with the further drawback that the nickel contains substantial amounts of hydrogen so that large amounts of gas are evolved during the melting operation giving rise to an article with more or less great cavities and having a low mechanical strength.

Nickel is also known commercially in a pulverulent form. Such nickel may be obtained by the reduction of finely divided nickel oxide by means of reducing gases such as hydrogen.

Where such pulverulent nickel is melted, the same disadvantages are experienced as in the melting processes referred to above.

Attempts have also been made to produce metallic articles from more or less finely subdivided metals by a method which avoids the melting operation and the contamination of the material involved therein and consists in subjecting the metal to a sintering treatment by heating to below the melting point, which heating operation may be assisted by the application of mechanical pressure before, during or after the heating.

While such a sintering operation has been carried through successfully for example with iron, it has been a complete failure in the case of nickel. Even when attempting to produce nickel articles by consolidating by sintering the pulverulent nickel of highest purity which is obtained by the reduction of nickel oxide, products are obtained which are sintered onlyincompletely and thus have a low mechanical strength which is insuflicient for practical purposes. For example, when such nickel articles are subjected to a rolling or forging treatment, they are always liable to become destroyed by cracks or'fissures- All past experiences have thus led to the conclusion that it is absolutely necessary, in order to obtain nickel articles of sumciently high strength, to have small amounts of manganese or magnesium present therein. Even the so-called pure nickel articles of commerce, such as are widely used in the chemical industry as well as for household and other purposes, never consist of pure nickel, but always contain only up to 98 or 99 per cent of nickel and in addition thereto manganese, and often also magnesium, copper and cobalt.

These additions as well as carbon and sulphur tend to reduce the resistance of the nickel articles to corrosion.

The aforesaid impurities of commercial nickel articles not only lead to the disadvantages re,-

ferred to in the foregoing, but they involve the further drawback that nickel could hitherto be welded only with difficulty, if at all, and the welding seams were often very brittle due to occluded gases and in any case of inferior strength.

Similar considerations apply, of course, to alloys of nickel, more particularly with iron, chromium, larger amounts of manganese, copper, or several of these metals. All alloys of this kind hitherto available in commerce have been-obtained by way of a melting operation.

In the course of the last years, finely sub-- divided nickel has become commercially available which is produced by thermally decomposing nickel carbonyl in the free space of a vessel heated to decomposition temperature, for example in accordance with the United States Patent No. 1,759,661. This nickel is of about the same degree of purity as the nickel obtained by the reduction of nickel oxide. hitherto been assumed that the nickel obtained from nickel carbonyl would have the same properties as the latter kind of nickel, and it has been converted into nickel articles or nickel alloy articles exclusively by the method of melting.

It was therefore highly surprising when we discovered that the nickel obtained from nickel. carbonyl constitutes an excellent material for the production of metal articles by the sintering method, provided certain precautions are taken which we shall explain below. It is this discovery that the present invention is based upon.

Nickel obtained by the thermal decomposition of nickel carbonyl in the free space of a heated vessel is characterized by being a fine powder. Analysis shows that it is free from manganese, magnesium, copper, silicon and phosphorus, and that it contains less than 0.002 per cent of sulphur. Its carbon content is usually very low, for example up to 0.03 per cent, though in some cases it may amount to 0.2 per cent or even more. It is this material that we make use of accord ing to our present invention.

Pure nickel articles are obtained by our process from this material which are characterized by the following properties: They contain at least 99.9 per cent of nickel, are free from manganese, magnesium, copper, silicon and phosphorus and do not contain more than 0.03 per cent of carbon and not more than 0.002 per cent of sulphur. As a result of this extreme purity, our new nickel articles can be welded without any difllculty, and the welding seams have the same mechanical strength as the remaining portions of the material. Our new nickel articles are further characterized by a particularly high softness or ductility, whereby they are easily worked in the cold as well as in the warm. They are particularly adapted for being stamped or rolled without suffering from fissures or cracks. In view of their quite peculiar and outstanding properties, our new nickel articles are eminently suitable, for example for use as anodes for electroplating with nickel, since the solutions remain sufficiently pure for a long time and the nickel precipitate produced on the cathode is more uniform, and for the production of nickel wire for the construction of thermionic valves and the like, since no occluded gases or other noxious substances are given off in vacuo.

The same kind of nickel is made use of for the production of alloys in accordance with the present invention. These alloys contain, in addition to nickel, one or more of the metals iron, chromium, copper and manganese. They are It has therefore further characterized by a sulphur content of less than 0.002 per cent and a carbon content of less than 0.3 per cent, preferably below 0.2 per cent. They possess a high mechanical strength so that they can be rolled in the cold and, especially in the case of alloys containing iron, excellent magnetic and electric properties.

In the case of nickel-iron alloys the iron content usually ranges between 40 and 75 per cent; the content in manganese in the case-f nickelmanganese alloys usually ranges between 0.1 and 2 or 3'per cent, while in the case of nickel chromium alloys the chromium content ranges as a rule between 15 and 25 per cent. It should be understood, however, that percentages outside these ranges may be used in some cases.

We shall now proceed to explain in detail the process by whichthe new metal articles according to the present invention are produced. This process has been disclosed in our application for patent, Ser. No. 348,113, filed March 18, 1929, of which this application is a'cqntinuation-in-part. As has been set forth in the said application, we have found that nickel or nickel alloy articles far superior to those hitherto known are obtained by subjecting nickel powder obtained directly by the thermal decomposition of nickel carbonyl, to

a sintering treatment by heat accompanied or followed by a mechanical pressure treatment such as rolling or forging.

In determining the conditions necessary for said sintering treatment, due regard must be had to the condition of the particles of the nickel powder to be treated. It is not only necessary that the nickel powder should correspond to the chemical composition indicated above, but regard must also be had to the average size of the particles which should not exceed 10 mu and preferably range between 0.5 and 5 mu. The weight of 1 liter of the powder should preferably be between 3 and 4 kilograms.

When the nickel powder contains more carbon than indicated above, i. e., more than 0.03 per cent, it must either be subjected to a-preliminary treatment to remove the carbon, as for example by treating in an atmosphere of hydrogen or by heating together with a nickel powder which is free from carbon but contains suflicient oxygen to combine with the carbon, or the sintering by heat is conducted under such conditions that the carbon is removed.

When preparing nickel alloy articles, the alloy metals must also be as pure as possible. The average size of their particles should not exceed 100 mu, in order to produce articles of a sufficiently high mechanical strength.

Regard must also be had to the surface condition of the metallic particles to be sintered. It will be readily understood that the said particles combine the more readily with each other, the less their surface is contaminated, for example with metallic oxides. Even an extremely thin superficial layer of metallic oxides may exert a great influence in this respect.

The sintering by heat according to the present invention is effected by subjecting the metallic powder to the action of high temperatures below the melting point of any constituent thereof, which treatment is preferably carried out in an atmosphere of inert or reducing gas in order to avoid oxidation of the metal. In this heat treatment the temperature should be at least 300 C. and preferably ranges up to about 1200 C. The time necessary for effecting sintering depends largely on the temperature employed. Thus,

2,159,804 when working at 500 c., the time required will preferably conducted slowly, because the heat conductivity of the metallic powder is low and too rapid heating of the mass might therefore lead to sintering of the outer portions of the mass only while the interior does not yet sinter; thereby cracks might be formed in the mass. Simultaneously with such heat treatment the mass may be subjected to the action of mechanical pressure, for example by pressing it by means of a suitable piston. We prefer, however, to apply a treatment 20 by mechanical pressure, as for example forging or rolling to the mass after it has been sintered and consolidated by heat. The mechanical pressure applied may be as low as 300 kilograms per centimeter. However, we prefer to employ higher pressures of the order of several thousand kilograms and may use pressures as high as 16.000 kilograms per square centimeter or even more.

According to our present invention, the metallic powder can be worked up into large metal ingots, which can be easily converted into articles of the desired shape, for instance by sawing, forging. rolling, stamping or filing. Articles of the desired shape, such as sheets, plates, tubes, rods or the like can also be produced directly by subjecting the nickel powder to the sintering process by heat and pressure treatment in suitable moulds. The individual particles of the nickel are preferably first brought into intimate mutual contact by shaking, tapping or ramming the powder into the mould.

The nickel material used for the production of the metal articles is, as already mentioned. the finely divided nickel powder prepared directly in the form of powder from nickel carbonyl. Similarly, when a nickel-iron alloy is to be produced, the iron powder is preferably that which is obtained directly in the form of powder from iron 'carbonyl.

In the course of the last years several processes for preparing such powders have become known. Some such processes have been described, for example, in the specifications of the United States Patent Nos. 1,7 ,659 and 1,759,661 and in the British Patent Nos. 269,677 and 281,963. Also mixtures of metallic powders obtainable from mixtures of metal carbonyls, for example from a mixture of iron and nickel carbonyl, may be used. Mixtures of several nickel powders prepared from nickel carbonyl and having grains of different sizes may also be used for the said purpose.

By the addition of appropriate alloy substances to the nickel powder the magnetic properties of the resulting metal articles can be altered extensively; thus a material very useful for the arming and winding of cables is obtained by mixing the nickel powder from nickel carbonyl with iron powder before it is worked up into bands.

The process according to the present invention has the great advantage that the metallic powders can be converted into solid pieces far more quickly and easily, by heat and mechanical pressure, than is the case with metals prepared in other ways, such as are obtained by the reduction of their pulverulent oxides in the usual manner, and that the resulting articles have a high mechanical strength. The said advantages are mainly due to the particularly uniform size and the ball-like or leaflet-like form of the particles of the nickel prepared from nickel carbonyl. A further advantage of the nickel powder prepared in this manner is that it is non-pyrophoric and therefore is not liable to suffer ignition and does not cause danger to life and property in the working into nickel articles. Owing to the aforesaid properties of the nickel powder, the articles prepared according to the present invention have the great advantage of being uniform throughout.

It should be noted that it is generally not very advantageous to use the nickel alloy articles according to our present invention for cores for electromagnets or the like, especially such as are operated with high frequency currents, without suitably subdividing them by arrangement in plates or the like, because they may give rise to considerable eddy current losses due to their being free from insulating inclusions, such as oxidic layers on the particles of the nickel powder.

The following examples will further illustrate the nature of the invention, but the invention is not restricted to these examples. The parts are by weight.

Example 1 21.5 parts of iron powder from iron carbonyl are thoroughly mixed with 78.5 parts of nickel powder from nickel carbonyl, in a mixing drum, and then placed in an iron mould and heated to 1100 C. in a current of hydrogen. The still glowing sintered ingot is rolled out into a sheet, 0.2 millimeter thick, without intermediate annealing.

Example 2 Finely divided nickel powder, prepared from nickel carbonyl, is heated at 500 C. for 24 hours in a current of hydrogen, and is then pressed. under a pressure of 40 kilograms per square centimeter, in a cylindrical mould. The resulting block has a porosity of 30 per cent and can be sawn into plates which may be employed, for example, for filtering strongly alkaline liquids.

Example 3 100 kilograms of nickel powder obtained from nickel carbonyl are pressed into a briquette and heated to 1200 C. for 2 hours in a furnace, through which a current of hydrogen is passed. The material is then rolled both while still hot and in the cold, sheet nickel being thus obtained.

Example 4 100 kilograms of nickel powder obtained from nickel carbonyl and containing 0.2 per cent of carbon are mixed with 100 kilograms of nickel powder obtained from nickel carbonyl and containing 0.25 per cent of oxygen. The mixture is heated for 4 hours at 1200 C. in a refractory mould, rolled while still hot, quenched, and rolled in the cold into a sheet of 0.5 millimeter thickness.

Example 5 A mixture of nickel carbonyl and iron carbonyl containing nickel and iron in equal amounts by weight is evaporated and decomposed at 260 C. in the free space of a heated vessel. A metal powder is obtained which contains 48.8 per cent of nickel, 48.8 per cent of iron, 1.2 per cent of carbon and 1.2 per cent of oxygen.

A portion of this powder is moistened with water and dried at 150 C. It then contains 47.9

per cent of nickel, 47.9 per cent of iron, 1.2 per cent of carbon and 3 per cent of oxygen.

100 kilograms of the powder initially obtained are mixed with 80 kilograms of the powder enriched in oxygen. The mixture is filled into a mould made of refractory material and heated for 4 hours at 1200 C. while excluding air. The sintered block is forged into bars which are rolled, while warm, into bands of 5 millimeters thickness. The bands are rolled in the cold to a thickness of 1.2 millimeters, heated for 2 hours at 900 C. in an atmosphere of hydrogen, and further rolled in the cold to a thickness of 0.35 millimeter. They are then made into coils and heated for 3 hours at 1000 C. in an atmosphere of hydrogen. The resulting material possesses an initial permeability of 5000, a maximum permeability of 65,000 and a coercive power of 0.03 Gauss.

Example 6 100 kilograms of nickel powder obtained from nickel carbonyl and containing 1 per cent of carbon is heated in a refractory mould for 12 hours at between 700 and 750 C. in an atmosphere of hydrogen which has been moistened with water at 30 C., and then further heated for hours at 1200 C. in dry hydrogen. The material is then rolled, first while still hot and then in the cold. Thereafter carbon can no longer be detected in the material by analysis.

Example 7 100 kilograms of nickel powder obtained from nickel canbonyl and containing 0.05 per cent of carbon are decarburized by heating in moist hydrogen in the manner described in Example 6 and then heated for 12 hours at 1200 C. in an atmosphere of pure nitrogen. The material is then rolled into wire, which contains less than 0.01 per cent of carbon and does not give off gases when heated in vacuo.

Example 8 99.5 kilograms of nickel powder obtained from nickel carbonyl and containing 0.03 per cent of carbon are mixed with 0.5 kilogram of manganese powder and heated for 10 hours at 1200 C., in

an atmosphere of dry hydrogen. The material is rolled into bars while hot and then quenched in cold water. The extensibility of the resulting material is at least 10 per cent higher than that of the material hitherto available in commerce which has substantially the same composition.

Example 9 60 parts of nickel powder obtained from nickel carbonyl are mixed with 40 parts of copper powder obtained by precipitation by means of zinc dust from a copper sulphate solution. The mixture is heated for 8 hours at 1000 C. in a current of hydrogen. The sintered block which has an apparent specific gravity of 6.6, is rolled at 1000" C. into a sheet of 2 millimeters thickness. The resulting material is much more resistant to corrosion than commercial Monel metal which is produced by a melting operation; thus, its resistance against the attack by urea, or caustic soda solution, or sulphuric acid is from 10 to per cent greater than that of commercial Monel metal.

What we claim is:

l. The process of producing nickel qticles containing not more than 0.03% of carbon which comprises heating to a sintering temperature a nickel powder obtained directly by the thermal decomposition of nickel carbonyl, said nickel powder being free from manganese, magnesium, copper, silicon and phosphorus, containing not more than 0.002 per cent of sulphur and having an average size of the particles not exceeding 10 mu, said heating operation resulting in consolidation of the nickel powder into a nickel article, said consolidation being assisted by the application of mechanical pressure at a time following the beginning of the heating.

2. Nickel articles obtained by a process as claimed in claim 1, containing at least 99.9 per cent of nickel, being free from manganese, magnesium, copper, silicon and phosphorus, containing not more than 0.002 per cent of sulphur, and capable of being welded and of being rolled in the cold.

LEO SCHLECHT. WALTER SCHUBARDT. 

